without using special tools like respin and archiso

What do you exactly mean with this?

• Can we suggest any package/tool that you have to install?
• Did you intend to convey a solution that’s independent of an existing distro?
• Do you want the custom distro/iso to only do its thing until installation? Or are you perhaps interested in something more declarative that can continue to exist and be (one of) the primary means to config your system?
• Could you explain to us how your envisioned solution looks like?

Sorry for asking these questions, but it was either this or a very very long post satisfying all kinds of different criteria. Thanks you in advance for answering any of the questions!